Iron chelate compound of tris(hydroxymethyl)phosphine oxide and nitrilotriacetic acid or alkali metal salts

ABSTRACT

MIXTURES OF TRIS(HYDROXYMETHYL) PHOSPHINE OXIDE, AND NITRILOTRIACETIC ACID AS WELL AS THE ALKALI METAL SALTS THEREOF, EXHIBIT MARKED SYNERGISM AS SEQUESTRANT COMPOSITIONS OVER A BROAD PH RANGE. THE SEQUESTRANT COMPOSITIONS ARE USEFUL AS ADDITIVES FOR DETERGENTS, METAL CLEANING BATHS, PEROXIDE COMPOSITIONS AND DYES. THE C HELATE PRODUCTS ARE USEFUL IN THE FIELD OF AGRICULTURE FOR THE INTRODUCTION OF TRACE ELEMENTS INTO PLANT LIFE AND ESPECIALLY IN THE TREATMENT OF IRON CHLOROSIS IN PLANTS.

3,780,079 Patented Dec. 18, 1073 Ffice IRON CHIELATE COMPOUND OFTRISMYDRDXY- METHYLWHOSPHINE OXIDE AND NTTRILOTRll- ACETIC ACHD R ALKALTMETAL SALTS Ronald H. Carlson, Lewiston, N.Y., assignor to HookerChemical Corporation, Niagara Falls, N.Y.

No Drawing. Application July 13, 1970, Ser. No. 54,660,

now Patent No. 3,655,573, which is a continuat on-1npart of abandonedapplication Ser. No. 680,011, Nov. 2, 1967. Divided and this applicationSept. 27, 1971, Ser. No. 180,204

lint. 1C1. C071 /02 11.0. Cl. 260 l39 R 3 Claims ABSTRACT OF THEDISCLOSURE Mixtures of tris(hydroxymethyl)phosphine oxide, andnitrilotriacetic acid as well as the alkali metal salts thereof, exhibitmarked synergism as sequestrant compositions over a broad pH range. Thesequestrant compositions are useful as additives for detergents, metalcleaning baths, peroxide compositions and dyes. The chelate products areuseful in the field of agriculture for the introduction of traceelements into plant life and especially in the treatment of ironchlorosis in plants.

RELATED APPLICATIONS This is a division of application Ser. No. 54,662,filed July 13, 1970, now US. Pat. No. 3,655,573 which is acontinuation-in-part of Ser. No. 680,011, filed Nov. 2, 1967 and nowabandoned.

BACKGROUND OF THE INVENTION The invention relates to synergisticsequestrant mixtures, their use and the chelated products thereof.

The use of complexing agents which combine with metal ions in solutionto form soluble complexes (which agents are commonly referred to assequestrants) is of great importance in many industrial processesinasmuch as it may prevent undesired precipitation reactions fromoccuring. For example, sequestration of calcium is important in watertreatment and in laundry solutions for controlling hardness of thewater. Sequestration of the heavy metals such as copper and nickel isessential in such areas as textile processing and metal cleaning andfinishing. Not all sequestrants, however, are equally eflective, theiractivity varying with their structures and the conditions under whichthey are used; for example, the common carboxylic acid sequestrants areoften inelfective in preventing ferric ion precipitation from alkalinesolutions of pH greater than 8.

The commercial utilization of water-soluble chelating compounds inagricultural applications to provide trace elements for plant growth iswell known. Likewise, the treatment of plants suifering from chlorosisas a result of growth in alkaline soils devoid of sufiicientassimilatable iron is known. Various chelating agents have been employedin the past to correct iron deficiencies in plants, the water solubiiltyof chelated metal ions affords the primary route for potentialassimilation into a plant structure.

Ethylenediaminetetraacetic acid (EDTA) has been employed in the past fortreatment of iron deficiencies of citrus trees under acid conditions.The EDTA iron chelates are not stable in neutral and alkaline media. Thedevelopment of sequestrants which may be employed in acid media as wellas alkaline media is significant not only for agricultural application,but for use in the detergent field, metal cleaning field, textile anddye industry and as stabilizers for organic and inorganic peroxides.

2 SUMMARY OF THE INVENTION In accordance with the instant invention,there is provided compositions of matter comprisingtris(hydroxymethyl)phosphine oxide and at least one member selected fromthe group consisting of nitrilotriacetic acid, and the alkali metalsalts thereof, in mole ratio of about 10/90 to 10.

Furthermore, in accordance with the instant invention, there is provideda process for sequestering metal ions from aqueous solution over a pHrange of about 4 to 11 by reacting the sequestrant mixture of thisinvention with metal ions.

Also, this invention provides novel compositions of matter comprisingthe sequestered metal ion derivatives of the seuestrant mixtures of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION Mixtures oftris(hydroxymethyl)phosphine oxide (THPO) and nitrilotriacetic acid(NTA) and its alkali metal salts unexpectedly display marked synergisticaction as a sequestrant composition in mole ratios within the range fromabout 10/90 to 90/ 10, generally at a pH of from 4 to 11.

The metal ions which may be sequestered by the composition of thisinvention are those cations having a valence of two or more, such as theions of chromium, copper, nickel, tin, aluminum, cobalt, platinum,palladium, rhodium, iridium, ruthenium, osmium, zirconium, hafnium, therare earths such as gadolinium, europium, neodymium, the actinides suchas uranium, and especially iron in the ferric (Fe+ state.

The tris(hydroxymethyl)phosphine oxide component of the synergisticsequestrants mixture need not be introduced into an aqueous system forcontaining metal cations as such, because it may be formed in situ inknown manner from various known precursors, such astris(hydroxymethyl)phosphine and tetrakis(hydroxymethyDphosphoninmhalide. Generally, at a pH above 7, thetetrakis(hydroxymethyl)phosphonium salts are converted to thecorresponding tris(hydroxymethyl)ph0sphine which undergoes oxidation toproduce the phosphine oxide.

The nitri-lotriacetic acid component of the sequestrant mixtures of thisinvention is preferably employed as its sodium (SNTA) or potassium(KNTA) salt to increase water solubility.

The synergistic action of the sequestrant compositions of this inventionvaries with the pH of the aqueous system as well as with the mole ratioof the components in the mixture. With a 50/50 mole ratio oftris(hydroxymethyl) phosphine oxide to trisodium nitriloacetate thesynergism of the sequestrant mixture toward ferric iron is evident at pHvalues from about 4 to about 11 while the effective pH range residesbetween about 6 to about 9 as the amount of tris(hydroxymethyl)phosphine oxide decreases to afford a 10/90 mole ratio ofreactants. As the amount of tris(hydroxymethyDphosphine oxide isincreased from a 50/50 mixture of the two reactants to a 90/10 moleratio, the effective pH range shifts to from about 7 to about 11.

The composition of this invention, when added to those solutions inwhich sequestration is desired, may be added as a solid or a solution.If it is desired to add said composition as a solution, the compositionmay be dissolved in water. From about 0.001 percent to about 50 percentconcentration (by weight) may be used, though it is preferred to usefrom about 0.01 to about 5 percent concentration (by weight), and it iseven more preferred to use from about 0.1 to about 3 percentconcentration (by weight). It is preferred to use said compositions assequestrants in aqueous solutions. When said composition is added to thesolution containing metal ions to be sequestered, the

temperature of said solution may be from about to about 100 degreescentrigrade, though it is preferred that said temperature be from about20 to about 70 degrees Centigrade, and it is even more preferred thatsaid solution be at ambient temperature.

The sequestrant mixture of this invention may be formulated either as anaqueous solution containing the two components in the desired ratio oras a solid mixture.

The sequestered iron chelate may also be employed as an aqueous solutionor as a solid. The ferric iron chelate is soluble in aqueous alkalinesolution in an amount exceeding 20 percent by weight, and contains morethan percent iron on a weight basis. Thus, when compared to the .ferriciron chelate of EDTA, which contains a relatively low percentage ofiron, 5-10 percent by weight, and which exhibits low solubility inalkaline solution, the sequestrant mixture of this invention presentsdecided advantages.

The solid ferric (Fe+ iron chelates of this invention are of the generalcomposition in which n, x, y and z are numbers greater than 0, and maybe prepared by mixing appropriate amounts of ferric chloride, sodiumhydroxide, tris(hydroxymethyl)phosphine oxide (THPO) andnitrilotriacetic acid (NTA) or a salt thereof in aqueous solution. Afterthe reaction is complete, the solid chelate may be forced from solutionby addition of a lower alkanol, such as ethanol or isopropanol. Theisolatedchelate is then dried and ground into a free-flowing brownpowder.

EXAMPLE 1 To 37.7 grams of 50 percent solution of a 50/50 mole mixtureof tris(hydroxymethyl)phosphine oxide and trisodium nitrilotriacetatemonohydrate (0.09 mole) was added 50 grams of aqueous solutioncontaining 14.5 grams (0.09 mole) of FeCl Sufiicient caustic was addedto this solution to adjust the pH of the solution to 7. A clear, darkmahogany solution was now present above a layer of settled solids. Thesolution was decanted and to it was added 120 milliliters of absoluteethanol to form a two phase system. The phases were separated bydecantation and the lower chelate phase was evaporated to dryness undervacuum (about 29 inches mercury absolute) at 50 C. Upon drying, a finelydivided free flowing mahogany powder was obtained. Infrared analysisshowed the product to contain both THPO and SNTA molecules. The productcontained 22.6 percent Fe and was soluble in water in excess of percentby weight. The pH of a 1 percent by weight aqueous solution of theproduct was 6.8. The chelate maintained its water solubility over a widepH range upon addition of sodium hydroxide to the aqueous solution.

EXAMPLE 2 The procedure of Example 1 was repeated with the exceptionthat isopropyl alcohol was used in place of ethyl alcohol to isolatedthe iron chelate product. The solid material recovered contained 12.9percent iron and exhibited water solubility in excess of 20 percent byweight, maintaining its water solubility from pH 4 to about 12. The pHof a 1 percent solution was 6.7.

4 EXAMPLE 3 The sequestering efficiency of the sequestrant mixtures ofthis invention as well as the individual sequestrants were determined bytitrating an aqueous solution 0.5 molar in FeCl dropwise into a stirred50 gram aqueous solution containing 0.5 gram of dissolved sequestrantuntil the end point was reached as observed by a perceptible permamenthaze in the solution. The pH of the solution of dissolved sequestrantwas initially adjusted to the desired point and maintained at thespecified pH during the titration by addition of aqueous sodiumhydroxide as needed to control the hydrogen ion concentration.

The sequestering efliciency was then calculated in terms of the poundsof ferric ion sequestered per 100 pounds of sequestrant. A sequesteringeificiency designation of 1.00 represents 7.1 pounds of ferric ionsequestered by 100 pounds of sequestrant.

The data presented in Table I compare the sequestering efficiency oftris (hydroxymethyl)phosphine oxide (THPO) and trisodiumnitrilotriacetate (SNTA) and mixtures of these two sequestrants in theratios indicated at the stated pH, for ferric ion. The mole ratio of thecomponents of the synergistic sequestrant mixture is within the rangefrom 10/90 to /10.

TABLE I THPO/SNTA THPO SNTA 10/90 50/50 90/10 It is clear from the datapresented in Table I that mixtures of tri(hydroxymethyl)phosphine oxideand trisodium nitrilotriacetate exhibit synergistic activity in thesequestration of the ferric ion at those pH values from 4-11 for the5'0/50 mxture; from 6-9 for the 10/90 mixture; and from 7-11 for the 90/10 mixture.

The most pronounced synergistic activity of the sequestran mixture ofthis invention is demonstrated by the 50/50 mixture at pH values fromabout 5 to about 10, while the 10/90 mixture exhibits its greatestsynergistic activity at about pH 9, and the 90/10 mixture is mosteffective between a pH of about 8 to 10.

To further place the instance invention in perspective, the sequesteringefficiencies of several known sequestrants for the ferric ion arepresented in Table H. The abbreviations employed are as follows:

Disodium iminodiacetate-SIDA Sodium tripolyphosphate-STPP Tetrasodiumethylene diaminetetraacetateSEDTA Glucom'c acid Trisodiumhydroxyethyl-ethylenediaminetriacetate- SHEDTA Pentasodiumnitrilotrimethylene phosphonate--SNTMP Pentasodiumdiethylenetriaminepentaacetate-SDTPA From a comparison of thesequestering efliciencies of the known sequestrants presented in TableII, with the synergistic seqnestrant mixture THPO/SNTA presented inTable I, it is apparent that the mixed sequestrant of the instantinvention provides completely unexpected activity toward the ferric ion.

What is claimed is:

1. An iron chelate compound prepared by reacting a mixture oftris(hydroxymethyDphosphine oxide and a member of the group consistingof nitrilotriacetic acid and an alkali metal salt thereof in mole ratioof about 10/90 to 90/10 with ferric ions in aqueous solution at a pH ofabout 7-9, and thereafter recovering said iron chelate compound as asolid product.

2. An iron chelate compound prepared by reacting a mixture oftris(hydroxymethyl)phosphine oxide and a member of the group consistingof nitrilotriacetic acid and an alkali metal salt thereof in mole ratioof about 50/50 to 90/10 with ferric ions in aqueous solution at a pH ofabout 9-11, and thereafter recovering said iron chelate compound as asolid product.

3. An iron chelate compound prepared by reacting a mixture oftris(hydroxymethyl)phosphine oxide and a member of the group consistingof nitrilotriacetic acid and an alkali metal salt thereof in mole ratioof about 50/50 with ferric ions in aqueous solution at a pH of about 4to 7, and thereafter recovering said iron chelate compound as a solidproduct.

References Cited UNITED STATES PATENTS 3,453,301 7/ 1969 Uhing 260-4393,477,953 11/1969 Carlson 260439 3,502,748 3/1970 Bersworth 260439WERTEN F. W. BELLAMY, Primary Examiner

